Genetic control of generative cell shape by DUO1 in Arabidopsis

Abstract

Key message The main features of generative cell morphogenesis, formation of a cytoplasmic projection and elongation of the GC body, operate through independent genetic pathways. Abstract Male gametogenesis in developing angiosperm pollen involves distinctive changes in cell morphogenesis. Re-shaping and elongation of the generative cell (GC) are linked to the formation of a GC cytoplasmic projection connected to the vegetative cell nucleus. Although genetic control of GC morphogenesis is unknown, we suspected the involvement of the germline-specific MYB transcription factor DUO POLLEN1 (DUO1). We used light and fluorescence microscopy to examine male germline development in pollen of wild-type Arabidopsis and in four allelic duo1 mutants expressing introduced cell markers. Our analysis shows that the undivided GC in duo1 pollen forms a cytoplasmic projection, but the cell body fails to elongate. In contrast GCs of cyclin-dependent kinase function mutants, which fail to divide like duo1 mutants, achieve normal morphogenesis. We conclude that DUO1 has an essential role in the elongation of the GC, but DUO1-independent pathways control the development of the GC cytoplasmic projection. The two main features of GC morphogenesis therefore operate through independently regulated genetic pathways.

The male germ unit association is independently regulated of GUM in Arabidopsis thaliana

“…Our analysis has well established that only CP elongation and development are required for the MGU association since if the GC body undergoes complete ( fbl17/cdka;1 ), partial ( duo2/duo3/daz1daz2) , or no ( duo1 ) morphogenesis in these different bicellular pollen mutants, an intact MGU can be formed (Figure 2 ; Figure S8–S10/S15 ). This further strengthens the discovery that the ontogeny of CP and GC elongation is independently regulated (Rauf et al, 2023 ).…”

“…We have analyzed and presented data from five independent homozygous marker individuals for each mutant. Our analysis shows that DUO1, FBL17, CDKA;1, DAZ1 DAZ2, DUO2, and DUO3 have no potential role in the MGU association, while their role in the development of the CP was excluded previously (Rauf et al, 2023 ).…”

“…The GC divides symmetrically by pollen mitosis‐II (PMII) into two SCs (SCs) of equal sizes. One of the SCs has a long CP, and the other has a small (87%) or two CPs of equal length (13%) in A. thaliana (Rauf et al, 2023 ). One of the SCs with long extension is physically linked with the vegetative nuclear membrane and forms the MGU at tricellular pollen stages (Late MGU) (Figure 2 , Movies S5 – S7 ).…”

“…Morphogenesis and elongation of the GC body and its CP are unique features of angiosperms. However, both developmental processes are regulated independently based on the analysis of multiple mutant alleles of DUO1 (Rauf et al, 2023 ). In that paper, we have shown that the male gametophyte bicellular pollen mutants ( duo1–1 , duo1–2 , duo1–3 , duo1–4 , cdka;1, fbl17 )/( daz1 daz2, duo2, duo3 ‐Rauf, 2017 ) form the CP, while here we confirmed the presence of MGU association, which exclude their potential role in this assemblage.…”